After emerging in late July and August and taking a short “summer hibernation,” Milbert’s are resuming activity before they overwinter. They, along with seven other hardy butterfly species in western Montana, have special “antifreeze chemicals” to survive winter. A cozy hibernaculum, which could be a hollow tree cavity, a crack in bark, or deep leaf litter, protects them from the elements. After literally chilling out for three months, they may be seen flying as early as mid-February on sunny, 50-degree days. In April, they are actively looking for food and mates. With little to no flowers around, they dine on oozing sap, as well as scat and mud for minerals and salt. All told, they can live nine to ten months. 

Milbert’s fly in wet areas near woodlands, moist pastures, marshes, woodland trails and roads across all of Canada and Alaska south of the tundra, all of the western United States, plus northeastern US.

Size: Wingspan 34-63 mm

Photo by: Kelly Dix on 8/28/21 in Lolo, MT